1. Field of the Invention
The present invention relates to a method of manufacturing a silicon single crystal, a silicon single crystal, and a wafer, and particularly to a method of manufacturing a silicon single crystal by the Czochralski method, a silicon single crystal, and a wafer.
2. Description of the Related Art
Power devices in cars, home appliances or the like should have a high breakdown voltage, and the resistance of the power device substrate affects the characteristics thereof. Therefore, a silicon wafer used as the substrate is required to be high in resistivity with a low variation of resistance.
When a p-type silicon single crystal is grown by the Czochralski method with boron being added as an impurity (dopant), boron is condensed in the silicon melt during growth of single crystal, because the segregation coefficient of boron with respect to the silicon single crystal is less than 1. Thus, the boron concentration in silicon single crystal increases with growth of the single crystal. Consequently, the resistivity of the silicon single crystal is varied at the tip and tail ends of a central axis during crystal growth (hereinafter referred to as a “central axis during crystal growth”) of the silicon single crystal (ingot).
As a conventional technique for suppressing such variation in axial resistivity due to segregation, a technique for suppressing axial variation in resistivity by adding phosphorus in an amount corresponding to 25 to 30% of the boron concentration to the initial silicon melt, and then growing the crystal by the Czochralski method is available. Japanese Patent No. 3931956 refers to this conventional technique.
The conventional technique described above, however, cannot realize the stricter radial uniformity of resistivity and stricter variation in resistivity among wafers, that are required in a silicon single crystal wafer for power device applications.